


Rebound

by PurrfecktlySinful



Category: Undertale (Video Game)
Genre: Bad Science, Bondage, Dissociation, Fontcest, M/M, Rape, Sans Has a Bad Time, Sanster, Soul Binding, Soul Rape, Soul Sex, bad touch gaster, gaster plots
Language: English
Status: In-Progress
Published: 2017-01-20
Updated: 2017-01-20
Packaged: 2018-09-18 18:03:44
Rating: Explicit
Warnings: Rape/Non-Con
Chapters: 1
Words: 4,079
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/9396788
Author URL: https://archiveofourown.org/users/PurrfecktlySinful/pseuds/PurrfecktlySinful
Summary: Gaster has an experiment in mind for his new Subject Sans, and Sans is in for a bad time.





	

**Author's Note:**

  * For [Askellie (NadaNine)](https://archiveofourown.org/users/NadaNine/gifts).



> This is a gift fic for my lovely friend, Askellie, whom is simultaneously one of the most encouraging and lovely people I know, but also a writer of great skill whom I definitely admire and look up to.
> 
> I hope this one came out okay and that you enjoy it my friend. The idea kinda grew a bit larger than I expected, so I had to split it up. The second part should come soon.

“ah!”

Sans cried out as Gaster continued to stroke the shaft of his cock. Pleasure and shame twisted and tore at his soul even as his body shuddered and arched, seeking more of the friction Gaster was providing. He shouldn’t be feeling like this, it shouldn’t feel good… The examination table was hard and painful under his back. There wasn’t even the illusion of intimacy, the smell of astringent in the air burned, the fluorescent lights were entirely too bright overhead and the room kept uncomfortably chill for the sake of sterility. Even Gaster’s hands were cold… colder than any monster’s hands had a right to be.

And yet despite it all, Sans couldn’t help the shivers and shudders that came with every touch, the flaring arousal that ran straight from his coalesced magic, to his pelvis and then to the rest of his body. He couldn’t hold back the low, breathy moans that escaped between his teeth. His hips bucked and thrust at the attention, even as he weakly struggled at the restraints that held his wrists and ankles bound to the table. 

He really was a disgusting creature, wasn’t he?

Gaster’s pale face hovered over him, haloed by the lighting behind it, the twin voids of his eye sockets peering down at Sans, the thin veneer of clinical detachment failing to hide the lust that burned, violet, in his eyes.

“How are you feeling, Sans?” He asked, his tone casual. If it wasn’t for the fact that he currently had Sans’ dick in his hand, it might have been the kind of question he would have expected over a cup of tea in Gaster’s office.

“fuck… you.” Sans spat between gasps “you obviously don’t ca—AAAH!”

Sans yelped in sudden pain as Gaster squeezed his throbbing member roughly at the base.

“Now Sans…” Gaster said “You agreed to this. I don’t touch your brother… and you cooperate with me in WHATEVER endeavors I pursue. I simply asked you a question.”

Sans looked away, stubbornly silent. He had no desire to give Gaster any more satisfaction than he already had.

His breath hitched and then fell into a low whine as Gaster resumed stroking Sans’ magic. The sick feeling in Sans’ soul intensified as the pleasure returned, buzzing through his bones.

“That’s okay. You’ll become more obedient as we spend more time together. For now, though, I need to see your soul.”

Sans jumped as Gaster laid a chilly hand on his bare sternum, his bones trembling at the scientist’s words.

What?

His SOUL?

He began to struggle anew, disgust and fear morphing into terror as he realized that Gaster wasn’t joking.

NO!

nonononono…

The litany ran in a low chant through his mind, his eye lights shrinking to pinpricks. Frightened beyond words, he shook his head frantically as Gaster watched him, unmoved by his struggles.

“Monster souls manifest whenever in a state of high emotion.” He intoned, as though giving a lecture. “Sometimes that can be due to arousal, other times in response to extreme antagonism, in preparation for battle.”

“no… please…” Sans finally managed, his voice cracking.

Gaster’s face split into a fanged grin that sent an icy chill down Sans’ spine. 

“Good thing we have plenty of both here, isn’t it?”

Sans’ terror spiked to a new high as Gaster gave another rough yank at Sans’ erect cock, sending a shock of sensation, amplified by his fear, through his small frame. There was a brief, bright flare of light as Sans’ soul manifested under his ribs.

Oh God no.

The small inverted heart jerked and stuttered, caught between intense fear and pleasure, fluttering indecisively within his ribcage. Releasing Sans’ cock and moving more quickly than Sans thought possible, Gaster’s hand slid up into his ribcage, effortlessly capturing the quivering organ and drawing it out into the open.

Sans whimpered, frozen, unable to anythingbut wait and see what Gaster would do next.

The scientist examined his prize with satisfaction. It was very small, appearing fragile in his hands, and he turned it over a few times before looking back up at Sans.

“Lets begin, then.” 

Saying this, Gaster began to rub the soul with his thumbs in firm, slow circles, squeezing it between his fingers.

Sans gasped, his mind blanking as a flood of tingling pleasure burst in, over and around him, making him feel warm from the inside out, agitating his magic even further. He didn’t want to feel this, but this was his soul… it was EVERYTHING that he was and there was nowhere left for him to hide.

Eyes still locked on Gaster, Sans looked on helplessly as the scientist continued to handle his soul, rubbing and stroking it, sending thrills and pulses of sensation through Sans’ body with every pass. Sans could feel the intent in those touches… Gaster’s intent, for him to feel intense pleasure, not for Sans’ own enjoyment, but for the sake of knowing he could force Sans to fall apart against his will, for control. It was a cold, impersonal, horrible pleasure that stole Sans’ ability to think or fight back, reducing him to a moaning, twitching, shuddering mess. Liquid magic seeped from the surface of the small organ, pooling and smearing under Gaster’s fingers as he continued to stimulate it. 

It wasn’t long before his soul was a dripping mess.

“That should be enough.” Gaster mused, shifting the soul into one hand and examining the azure magic dripping from the other. Smiling to himself, he brought his soiled fingers to his mouth and licked them clean with a glistening, oily looking tongue.

Sans slumped back onto the table. He could only lay there, body limp and ribs heaving during the small reprieve. His magic still burned through his bones and his cock still throbbed uncomfortably, his body craving release. However, the discomfort was almost welcome, a fitting punishment that Sans would willingly accept over the humiliating pleasure that had been forced on him till now.

Placing his free hand near his own chest, Gaster concentrated for a few moments. There was small flaring of magic as his soul appeared above his hand, already dripping with desire. Sans shifted when he saw this, his soul fluttering anxiously as he wondered what Gaster had in mind for him.

“Now for the real experiment. Theory says I should be able to achieve the results I desire… if I can appropriately control what happens next…”

Gaster brought his hands closer together, one carefully cradling his own soul, the other wrapped firmly around Sans’, the grip making Sans feel as though there was an uncomfortable weight pressing in on him from all sides. As they were brought closer together, Sans’ soul struggled weakly, pressing back, away from Gaster’s soul and into the hand that held it.

Sans could only watch with a growing dread, realizing he couldn’t stop what was about to happen. The internal litany returned.

nonononono…

Once they were within a few inches of each other, with only a small gap remaining between Gaster’s open palm and the hand clutching Sans’ soul, Gaster’s soul leapt forward, sensing the other, more vulnerable soul and pressing into it aggressively, completely overwhelming the smaller organ.

Sans cried out as a new, more intense wave of sensation and emotion ran over and through him like a wave, sweeping him up and carrying him away. Thoughts didn’t exist… HE didn’t exist, all he could feel was their raging emotions… his own fear, despair, loathing, and pleasure… surrounded and overpowered by Gaster’s lust and desire to dominate. He was vaguely aware of his body arching and straining against the straps around his limbs and of Gaster’s face, dusted violet, his own breathing quickening from the intimate contact of their souls as they continued to slide against each other. Their magics mingled and ran in a violet and blue swirled slick over his white hands before dripping wetly onto the floor.

Even in that overwhelming vortex, there was a concentrated center of reserved, cold impassivity. As both of their souls rubbed and sparked against each other, Gaster still maintained a locus of detatchment, though that, too, was beginning to crumble.

Something that felt like ice pierced Sans’ soul, pressing steadily, like a needle, deeper and deeper. His body jerked and Sans choked on a moan as whatever it was reached the center of his soul, where it flared and settled, a cold and hard point at his core.

He growled and released their souls. They remained hovering and dripping in place as Gaster dropped his slacks. Sans could see the thing that was Gaster’s cock between his legs. Thick at the base and tapering toward the tip, it squirmed, waving and eager. 

Sans Soul pulsed. No! He didn’t want that! The denial… Sans’ rejection of what Gaster wanted flared across their connection. There was no way he didn’t know Sans didn’t want this.

He just didn’t care.

Gaster slammed the emergency release next to the table and Sans felt his limbs come free from their restraints. Before he could process and respond, however, Gaster had him by the ankles and yanked him close, forcing himself in between Sans’ legs.

Sans could only hang on as the appendage quickly and effortlessly sought out and found his entrance, forcing its way in, making him shout in pain and shock. He could feel it, squirming and hot inside him, and he felt disgust even as his body shivered with the pleasure of being filled. It stretched him painfully as it drove further into him. Sans groaned, though the pain was nowhere near enough to douse the arousal that still burned in his bones. 

Gaster immediately set a punishing pace, thrusting hard and fast into Sans’ magic, already near his climax from the feedback through their linked souls. Sans’ distress only seemed to feed Gaster’s lust, making it burn hotter as his face contorted into something almost animalistic. Tears streaked Sans’ face and he moaned piteously as he felt his body being used without mercy, having just barely enough presence of mind to hope it would be over quickly.

With a final, shuddering thrust, Gaster hilted himself, spilling into Sans as his orgasm took him. The intensity of his climax ran like a whiplash through their connection, dragging Sans over the edge with him, his body clenching and convulsing around Gaster as he shuddered through his own peak. Somewhere close, there was a bright flash of azure and violet light as their souls also released, the emotions and sensations rebounding and intensifying over the soul link until Sans, finally pushed to his limit, passed out.

****************

Sans wasn’t sure how much time had gone by since he lost consciousness, but it couldn’t have been long. As the room came back into focus, he could see Gaster standing at the other end of the room, his back turned. There was no sign that anything out of place had happened, his lab coat crisp and white, his garments neatly arranged as they always were, completely formal and professional. Thoughts began to return slowly, tentatively… as though there were some reality his mind didn’t want to touch.

Cold.

He was cold. 

Sans shifted where he lay on the unforgiving table. Stars, everything hurt. His joints flared in pain with each movement. There was a chafing burn at his ankles and wrists. The fatigue was overwhelming, every bone in his body feeling leaden. His soul didn’t feel right either. It was an odd sensation, like there was something cold and hard wedged into his core.

What…?

Sans looked down at himself, eyes widening at the half dried mess of blue and purple fluids that still trickled and dripped over his naked bones. His femurs and pelvis also ached, throbbing up at him as a dull reminder of… of…

Sans remembered. The pieces snapped together and memory washed over him, clenching his soul in an icy grip of disgust and dread that felt like it would dust him right there on the spot.

With a sob, Sans curled in on himself, wishing he could force himself to descend back into the oblivion he had just risen from.

He remained that way for some time, arms wrapped around his knees, eyes staring into nothing. Gaster didn’t seem to notice, continuing his work unperturbed by Sans’ distress. It wasn’t long before he finished and turned his attention back to him. He made a sound of annoyance.

“Quit being so melodramatic.” Gaster’s cold voice cut across the space between them. Sans looked up despondently. Gaster stared back at him, impassive. “Sit up.”

Sans considered disobeying at first. He could just tell Gaster to fuck off before leaving and then never come back. But then what of his promise? The Royal scientist had enough power that getting a monster—Papyrus for example—to “volunteer” to assist with some experiment or other wouldn’t be all that difficult. Oh, no big deal, just some innocent tests, thank you very much. From there it wouldn’t be hard at all for Gaster to get his brother alone and… 

Sans’ soul pulsed.

Anything but that.

Sans had to make sure Papyrus stayed safe.

Trembling, Sans slowly uncurled himself and sat up, clutching at the edge of the hard surface to either side of him as Gaster approached. He felt sick. He didn’t want the scientist anywhere near him.

“How are you feeling?” Gaster asked cooly

Sans grimaced at him in a pale mockery of a smile.

“heh. like i’ve got one hell a bone to pick…” 

You skeevy fuck how can you be so damned calm after you just fuckin forced me to…

Sans felt like he might throw up.

“If you can answer like that then you must be well enough.” Gaster answered dryly. “Now, may I please see your soul?”

Sans’ head jerked up and his eye light shrunk to pinpricks. Even with the ‘please’, there was no way that was a request. He felt panic begin to rise, his magic flaring defensively as he shook his head frantically.

“Oh be still.” Gaster snapped irritably “I just want to look at it this time, nothing more.” When Sans continued to shake his head in the negative, Gaster sighed. “Fine, then. I was going to wait till later to test this, but I guess we get to do this now.”

Gaster reached out with one hand, and Sans instinctively flinched away from it. He felt a sharp tug at this core, and to his horror, his soul manifested in the space between his sternum and Gaster’s hand. 

What the hell had happened to it!?

The normally pristine, smooth surface of his soul was now marred by dozens of purple threadlike structures that wrapped around it in a crisscross pattern. It looked for all the world like someone had wrapped string around the small organ. All of the threads seem to radiate from a single point, where Sans could see them come together and dive down in a thin line, into his soul, ending in a pulsing point of light in the center. That’s why his soul didn’t feel right. It was small and cold and hard and… WRONG is the only word Sans could bring to mind.

It was too much.

Sans began to hyperventilate.

“Stop that.” Gaster ordered

“AAAH!”

Pain flared, sharp and bright through his entire body as the threads surrounding his soul squeezed hard. Sans gasped as he was snapped back to reality. They could hurt him. These things were wrapped around his soul and he couldn’t get them off and they could HURT him.

Gaster was smiling. Sans hated that smile.

“Well that’s definitely a satisfactory response. It looks like the magic took well enough. In the passion of the moment, I was unsure of whether I had implanted the soul fragment properly.”

Sans looked from his soul to Gaster and then back.

“what did you do to it?” Sans asked, completely dismayed.

“I transferred a fragment of my soul into yours.” Gaster explained. He didn’t even look at Sans, returning to his notes to scribble down his observations. “It should offer some additional benefits to our arrangement. It can be used in a number of ways. Administering punishment is one of them. It is an untried method of monitoring and control, but I am satisfied with the results so far.” 

Sans felt his soul sink. Could this possibly get any worse?

“I need another monster to work with.” Gaster mused to himself as Sans’ soul faded and then disappeared, returning to it’s owner. ”I shall have to think the matter over.” He gave Sans a dismissive look “Clean yourself and the lab up and go home for the day. I fully expect you to be here for your next shift.”

Without a second glance, Gaster left the room.

Sans started as the door shut, the sound jarring in the now quiet lab. He sat for a long time, unthinking, staring at the violet and blue slick on the floor. Now that Gaster had gone, an unexpected numbness had descended on him, dulling the swirling emotions within him. He didn’t want to think. He knew he would fall to pieces if he allowed himself to dwell on what had happened and how he felt about it. All he had to do was focus on the next thing… don’t think too hard about it… just do what needed to be done. He didn’t even need to get dressed to do it.

Stand up. Get the cleaning supplies. Sterilize the table. Mop the floor.

He watched, fascinated, as the soaked up magic seeped out of the mop and into the dirty water each time he rinsed it, the colors dissolving and fading away in little tendrils into the murky water, all evidence of what had happend disappearing as he cleaned. 

Of what had happened to him…

Sans wasn’t know how long he blanked out for. All he knew is that when he came back to himself, he was still leaning against the handle of the mop in the bucket, the previously scalding water now stone cold. He took a shuddering breath, feeling a flash of annoyance at himself for the lapse, before changing the water and finishing the floor. 

Once the cleaning was done, he finally made his way to the adjoining room and the shower within. He ran it hot, almost hotter than even his temperature-resistant bones could stand, and certainly hot enough to burn a more fleshy monster. That was okay. Right now, hot was good. Methodically he cleaned himself, washing away the caked and smeared release coating his bones, paying extra attention to the joints and crevices. He was diligent and thorough, and if he scrubbed just a little to hard… hard enough to abrade the bone, that was okay too.

It felt good to have his thick Jacket around him again. He took a moment to savor the comfort of the garment, burying his hands in his pockets and sinking his head down into the soft fabric of the neckline. He breathed in the familiar scent of clean snow and the detergent Papyrus liked to use on laundry day. It felt like a shield. While he had it on, he could be himself, despite all that had happened.

Sans took a deep breath. That’s right. Just don’t think about it. Treat it like a bad dream. Time to go home. Home to Papyrus.

Sans reached out to the door before pausing, hand trembling an inch from the knob. He stared at the door like it was some obstacle to be overcome. After a few moments he reached up and pulled his hood over his head, hiding his face.

Better.

Forcing himself to relax into his signature slouch, Sans opened the door and left the room. Just the end to another boring workshift.

*****************

Gaster watched Sans leave through one of the many cameras scattered about the lab.

He liked his new experiment. Something about the small skeleton was the perfect solution for the ache of boredom that had been plaguing him lately.

Speaking of.

He closed his eyes, reaching out through their new link, testing and probing while being cautious to keep the connection going in one direction only.

Blankness. Numbness. Weariness. Barely contained sadness, fear and self loathing—Gaster smiled at that. He could sense slight annoyance at being over warm, but also an unwillingness to remove the thick coat his subject was wearing. Vague impressions of heat and lava, red and brown stone that gradually changed to the blues, greens and blacks of Waterfall.

The link was working quite nicely.

Suddenly there were clearer impressions, flashes of vibrant imagery that were intriguing to say the least. He saw the bright teal of the echo flowers Sans passed almost as though he were standing next to him. That was curious. Why would that be?

Gaster got his answer when the subject passed through the wishing room. As he stopped to look up at the ceiling above, Gaster was struck with the beauty of the hundreds of gleaming gems above, glittering brightly in the darkness. He felt his own breath catch at the sight, and he felt a temporary sensation of calm and comfort that washed back through their connection.

Wait. No. That wasn’t right.

Gaster snapped the connection shut, taking a hard mental step back.

It was emotion. The stronger impressions came through because there were stronger emotional ties to them. 

How interesting… and dangerous.

He made a few more notes. He would have to be very careful not to let his subject’s emotional perception color his own. Emotion had no place in science.

Tentatively, Gaster re-opened the connection, once more reaching out to see what he could perceive.

Cold. Familiarity. Gaster could sense that the subject was in a place where eyesight was limited, but that he was relying on his intimate knowledge of the surrounding area to make his way towards home.

Oh yes, he did live in Snowdin, didn’t he?

Then something new. The impression that someone was approaching. A brief surge of apprehension… Fear… Dread… Then sudden recognition.

That’s when Gaster got his first glimpse of Papyrus.

The image in his mind was strikingly clear. Tall build with broad ribcage and shoulders, pristine bone covered by something that was like armor but way too revealing to offer much in the way of true protection. A red scarf that fluttered dramatically, with or without wind. He was very impressive as seen through his subject’s eyes.

Relief. Love. Devotion. Awe. Gaster felt all of these emotions so strongly that he very nearly had to close the connection again to preserve himself from being influenced. Instead he settled for dampening it a bit instead. 

A scolding which was taken in good nature, and then the sensation of a larger hand enveloping a smaller one.

With strictly enforced detatchment, Gaster was able to examine this new information more closely and he began to detect an undercurrent to these emotions, low and buring… was that… desire?

That was… OH… Now THAT was interesting. 

He certainly hadn’t expected that. Gaster knew the subject adored his brother and was fiercely protective of the younger skeleton, but he certainly had no idea there was any possibility that those feelings might be distinctly unbrotherly in nature.

Gaster made his decision right then and there.

He wanted Papyrus.

Of course this had nothing to do with the strong emotions that were drifting back through their soul connection. He was being perfectly rational. After all, wouldn’t it be better to have another skeleton as part of the experiment, to be used as a control or as an alternative subject b when subject a was indisposed?

And if he chose to take advantage of some additional benefits with his subjects, that was only his due for the advancements his research provided for all of monster-kind.

The only problem was that in his agreement with Sans, he had promised not to touch his brother.

Not that he planned on actually abiding by that stipulation. However, he wanted a better idea of how much control their link provided before he stepped over that line and risked any concerted backlash from his newest subject.

After some thought on the matter, Gaster smiled. 

Well, then. It was time to run some further tests to see how much he could do.

And he knew exactly how he was going to do it.


End file.
